Powdered metal gears are frequently used in pumps, such as gear pumps for example, as a lower cost alternative to machined steel gears. Generally, powdered metal gears perform very reliably in hydraulic gear pumps. Whenever powdered metal gears fail, it has been observed that the failures can be attributed to two potential causes. The first cause is generally, an improper heat-treatment during the manufacturing process, which results in brittleness of the powdered metal. The second cause of failure of a powdered metal gear is related to the design of the drive keyway for the connection of the drive gear to its shaft. This invention is directed at eliminating this second cause, and relates to an improved drive keyway in a powdered metal gear.
Typically, the drive keyways have inner side walls and end walls having planar surfaces which meet in sharp corners. The drive keyway is typically adapted to receive a key which is received partially in the drive keyway in the gear and the drive keyway in the machined metal shaft. It has been observed that a "sharp-cornered" keyway in a powdered metal gear is a major contributor of failures in the gear due to stress concentration in the sharp corners.
It is desirable to have a powdered metal gear that does not fail due to cracking that originates from stress concentration in the drive keyway. It is thus desirable to have a gear having a drive keyway that is not subjected to stress concentration in any localized area. It is further desirable that this drive keyway have a configuration that not only reduces stress concentration, but also minimizes any motion of the drive key in the axial direction. The present invention is directed to overcome one or more of the problems as set forth above.